Oil smoke puff on startup of rebuilt 3.2

[BGCarrera32]

Hi:

I have a 3.2 Carrera motor that had around 160k on the odo. I rebuilt the engine last winter. During the rebuild, I went to 98mm P's and C's, 9.5:1 effectively making a single plug 3.4. I reused the oil pump- my local 911 shop looked it over and said it was in super shape- one of the nicest he's seen in a teardown and to go ahead and reuse it after flushing it out (brake clean). He normally always replaces them when he does a rebuild.

A leakdown test performed at 500 mi says all cylinders 5%, I am told this will improve as the engine breaks in. Goetze rings were used on the JE Pistons.

My motor has around 1,500 miles on it now, and here's the issue- the car will puff a cloud of oil smoke at startup, sometimes a nice one depending on how long its been sitting or at what angle. In addition, this winter, I yanked the exhaust to do a custom header system. I also ran through the valves for a quick checkover, and after turning the engine over by hand, noticed the exhaust ports on cyls 1 and 4 (closest to the rear of the car) were wet with oil when I got underneath.

From what the supplier of the engine parts told me, this is an issue as old as the 911 itself- oil will seep past the pump gears and slowly fill a bit of the case (and the cylinders) creating that puff on startup. My local guy says that he sees this periodically on totally healthy engines (wet valves) and that some oil on startup is normal.

I believe all of the above to be true, however, the pre-rebuild motor NEVER did this. One thing I did do when cleaning the case was to remove and replace the pressure relief springs in the oil circuit.

Let's assume reusing my old oil pump did not create the condition I speak of, and the rings I believe are all fine and I took great care at installation- is it possible that oil seeping into the case or what I am seeing is the result of anything to do with the pressure springs (red arrows in the picture)? This oil puff problem is more of an annoyance than anything and it would be nice to mitigate it. I'm running Brad Penn 20w50.

Thoughts?
BG

[Steve@Rennsport]

BG,

There are many sources of oil that can contribute to the startup smoke that you see:

1) Slightly overfilled tank

2) Valve guides improperly fitting or with the wrong seals

3) Excessive piston top ring land clearances


Those are just a few but a starting point toward understanding what is going on.

Naturally, if the engine sits for a few weeks without starting, oil migrates from the tank to the engine case and with a higher oil level, the pistons are partly submerged which will cause a good-sized smoke cloud on initial startup.

[RichHawk]

My 100 mile 3.2 rebuild did it's first puff of smoke after sitting for 3 days. it never does it from overnight. Just another data point for you.

I can't find any way to blame the pressure relief system to smoke on startup. It might be in some part of the whole thing, but in no way that you could easily modify it to prevent the puff of smoke.

My reasoning is this: The oiling system is full of holes, so it can't maintain pressure without a spinning pump to force oil into the system to replace that which comes out of the cam sprayers, and crank shaft bearings. So when you turn off your engine, the oil pressure falls right to zero.
With no pressure standing in the pipes, oil won't move under any influence except gravity.

So gravity plus the oil tank being higher than the engine is the only way oil is going to move into the engine. Following the path of oil from the tank there are four places it can get back into the engine: Either of the oil pressure relief pistons, and either the oil scavenge pump, or oil pressure pump.

None of these paths are oil tight. They can't be. Their job is to pass oil, and to be able to move quickly. It's a side effect of their function that standing oil could dribble past given enough time. Modifying the relief pistons to include an oil tight seal (like an o-ring) would add a bunch of stiction to them, making them unable to move freely, and causing massive oil starvation if they stuck even slightly open. Can you say BAD IDEA?

If enough oil dribbles past then the oil level in the case rises to a point where oil is standing against the rings. They too can dribble oil if gravity has it's way with the oil long enough.

I don't like it any more than you. But I can't even think of any practical way of controlling this.
I've thought of relocating and raising the pressure relief pistons to above the tank oil level. (Impractical / requires heavy case modifications)
I've thought of check Valves in the oil return path (unreliable leaky in their own way, stiction could cause overpressure of the scavenge system)
and lastly I've thought of an auxiliary, electric powered scavenge pump that keeps the case oil level lower than piston rings when the engine is off. But I haven't even begun to flush that out fully.

in the end, I'm just going to live with it.

Richard

[Steve@Rennsport]

Richard,

FWIW,....this "problem" is fixable but its simply not cheap to do,.....

[BGCarrera32]

Well I ran it for the first time of the year yesterday and checked the oil level engine warm after about a 15 mile drive. T-stat to front cooler was open (lines warm). It definitely is not overfilled with oil, I am at about 1/4" above the 2 lower dots on the dipstick with engine at idle and warm. It sat for another day and when I started it this afternoon, it puffed. Not a big deal, but embarrassing on an engine I took great care in rebuilding.

Or so I thought I took great care...

The pistons were JE's using included rings from a well known supplier.
The same outfit did the heads, I had them use Teflon seals.

Hmmm...

Thanks again Steve for your advice over the years. Me thinks I better find something to buy from you soon...

[Steve@Rennsport]

Originally Posted by BGCarrera32

The pistons were JE's using included rings from a well known supplier. The same outfit did the heads, I had them use Teflon seals.

Hmmm...

Thanks again Steve for your advice over the years. Me thinks I better find something to buy from you soon...

You are quite welcome,....

Call me sometime about the other stuff,..........

[JeremyD]

What cams are you running? If you are running an aggressive cam with high lift and the shop that did the heads used the "normal valve guide seals" (apparently there is a normal, and shorter set) It can cause the valves to disturb the normal valve guide seals and you get this condition where you get a little above normal oil consumption and a little more smoke at start up.

[BGCarrera32]

Thanks Jeremy, I am running a 964 cam grind.

I am thinking something is up with the Teflon seals on some number of the valves perhaps. Like I stated above, I recently had the exhaust system off for an upgrade. I looked into the exhaust port of every head (for the heck of it) with a flashlight when I was farting around underneath the car on the creeper.

I proceeded to pull the valve covers and spark plugs, and do a valve adjustment just to spot things after 1,500 miles of break in. I rotated the engine around by hand a couple times. When I got back underneath the engine to continue with the exhaust that day, I noted that the back of exhaust valves 1 and 4 were wet with oil.

My guess is oil is wicking down the effected valve stems past the seals.

I am going to watch my oil consumption very carefully. What is an expected or tolerable oil consumption for a motor that should now be fully broken in?

[Steve@Rennsport]

FWIW,........

We rarely use Teflon guide seals for these very reasons,......high oil consumption. Everyone has an opinion about this, but I've had the best luck over the past 33+ years using factory guide seals. These are now Viton and they do a excellent job of controlling oil without starving the guides of lubrication.

Sometimes I do install teflon ones on 930 engines ONLY on the exhaust side for more lubrication because these run very hot.

[BGCarrera32]

Thanks. So assuming this is my issue...obviously I need to pull the engine. Would I have to go all the way back down to each head to replace the seals, or can it be done in situ?

[JFairman]

If the oil level is around the upper part of the range on the dipstick, is the exhaust valve seal submerged in oil after the motor has been silent for around 12 hours or so?

With only the top valve cover off you can see the oil level down there partway up the lower cover with a flashlight.
I may have used a mrror too.